Machines such as, for example, on-highway vocational vehicles, off-highway haul trucks, wheel loaders, motor graders, and other types of heavy machinery are used for a variety of tasks. These machines generally include a power source, which may embody, for example, an engine, such as a diesel engine, gasoline engine, or gaseous fuel-powered engine that provides the power required to complete these tasks. The power source may have a desired operating range, which may include those speeds and torques at which the power source experiences substantially stable and efficient operation. When operating outside the desired operating range, the power source can experience unstable operation such as, for example, overspeed situations, underspeed situations, lugging, and/or stalling. Efficiency losses may also be experienced by the power source when operating outside the desired operating range such as, for example, increased fuel consumption, increased exhaust emissions, increased power source temperatures, and/or decreased responsiveness.
To efficiently perform the variety of tasks assigned to the machine, the machine utilizes a transmission that is capable of transmitting the torque generated by the power source to one or more traction devices over a wide range of speeds. The transmission may include, for example, a mechanical transmission, an electric transmission, a hydraulic transmission, or any combination of these transmissions. The transmission may be capable of providing a desired output torque at a desired speed within its operating range by changing a ratio of an input rotation to an output rotation. Similar to the power source described above, the transmission may have a desired operating range at which the transmission experiences substantially stable and efficient operation. The desired operating range of the transmission may be different from the desired operating range of the power source. Similarly, a most stable or efficient operating range of a combined power source and transmission package may be different from either one of the individual transmission or power source desired operating ranges.
One method of attempting to improve a machine's efficiency is described in U.S. Pat. No. 6,436,005 (the '005 patent) issued to Bellinger on Aug. 20, 2002. The '005 patent describes a system having a control computer operable to determine a number of engine load/speed boundary conditions as a function of brake specific fuel consumption contours in relation to an engine output characteristic map. The control computer defines therefrom an undesirable engine operation region. As long as the engine is engaged with at least one of the gear ratios of a vehicle transmission, the control computer is operable to maintain or encourage engine operation outside of the undesirable engine operation region by changing an output ratio of the transmission.
Although the system of the '005 patent may provide a way to improve a vehicle's efficiency by using the vehicle transmission to maintain the engine within a region of desirable operation, it does not account for efficiency characteristics of the transmission. That is, although the control computer of the '005 patent may maximize efficiency of the engine by encouraging operation of the engine outside of the undesirable operation region, it is possible that the undesirable operation region of the engine overlaps with a desirable operation region of the transmission. In this situation, although engine efficiency may be improved, overall power train efficiency could be unaffected or even reduced.
The control system of the present disclosure solves one or more of the problems set forth above.